1. Field of the Invention
The present invention relates in general to an apparatus and method for controlling ignition timing in an internal combustion engine, and more particularly to a technique for detecting current control timing by determining a time from a standard position signal.
2. Description of the Related Art
In general, a cam sensor or a crank angle sensor is installed in an internal combustion engine and outputs a detecting signal for controlling ignition timing based on a standard piston position of each cylinder. Ignition timing is controlled by generating reference position signals based on the detecting signals output by these sensors.
Specifically, an engine load or an engine rotation speed decides ignition timing. On the other hand, a battery voltage decides an ignition time, which is converted into an energization angle based on the engine rotation speed. As a result, an ignition-starting timing is decided by ignition timing before the energization angle.
When a sensor outputting a single-angle signal for each single crank angle is installed in connection with the cam sensor or the crank angle sensor, the ignition-starting timing and the ignition timing are detected by counting the number of single-angle signals.
When the sensor outputting a single-angle signal has trouble or is not installed, the ignition-starting timing and the ignition timing cannot be determined by counting the number of single-angle signals after a reference position signal. Instead, the ignition timing is controlled based on the engine rotation speed. Passing/interrupting a current through an ignition coil is controlled by control timing, which is detected by counting time from a reference position signal.
When an ignition-starting timing to the ignition coil is decided by the ignition time and an energization angle, which is before the reference position signal just before the ignition timing, the ignition-starting timing is detected by counting a time from a previous reference position signal, i.e., a reference position signal just before the ignition timing. When the ignition coil is energized, the time at which current to the ignition coil is interrupted (i.e., the ignition timing) is determined by counting a time from a reference position signal REF just before the ignition timing, as shown in FIG. 4.
However, in the above ignition timing control, when the engine stalls after starting energization to the ignition coil and the reference position signal REF cannot be output, the ignition coil is energized until the current is interrupted after it is determined that the engine has stalled. As a result, the ignition coil is damaged by high temperature caused by the current.
A Japanese Patent Publication No. Heisei 10-47142, published on Feb. 17, 1998, exemplifies a previously proposed apparatus for controlling the ignition timing in an internal combustion engine. In the disclosure of the above-mentioned Japanese Patent Publication, when the crank angle sensor does not provide a usable detecting signal, the ignition timing is controlled by a detecting signal provided by the cam sensor. However, when the engine stalls after starting energization to the ignition coil and the reference position signal cannot be output, the ignition coil is energized until the current is interrupted after it is determined that the engine has stalled. As a result, the ignition coil is damaged by high temperature.